This invention concerns a heat treatment device for converting gaseous test samples into constituents determinable by a detector.
The test samples to be studied, frequently taken from the ambient air, may contain pollutants to be determined. However, such samples may be unwanted substances such as those produced in chemical processes. For simplicity, reference will be made to the pollutants with the understanding that the test sample may also contain other unwanted substances.
Pollutants in the ambient air can be determined in various ways. A detector is necessary that responds to the specific pollutants to be studied. In many cases, it is impossible to provide an appropriately sensitive detector, or the detectors available are not intended for a specific pollutant, but are sensitive to several components likewise present in the ambient air to be studied.
This so-called cross-sensitivity makes reliable evaluation of the actual amount of pollutant difficult. Efforts are therefore made to increase the selectivity of a pollutant measurement, for example by resolving the pollutant to be determined into components to which the following detector reacts specifically and without cross-sensitivity. One such possibility consists of subjecting the pollutant to a heat treatment (pyrolysis), by which the pollutant is converted into the widest variety of pyrolyzates, one of which is determined by the detector.
Such a device with which a test sample to be studied is subjected to pyrolysis is described in German Patent Application Disclosure No. 21 35 203.
According to German Patent Application No. 21 35 203, the sample to be studied is passed through a collector provided with an adsorbent in which the pollutant to be determined is concentrated. After the sample, the collector is introduced into a separate analyzer. This instrument has a pyrolysis furnace in which the collector is heated, with the pollutant it contains being driven off and decomposed pyrolytically, and with a liberated pyrolyis product being studied by a following measuring instrument.
The known device is used to determine the content of alcohol in the breath, so that hydrogen as a typical pyrolysis product, which is fed through a filter permeable to hydrogen, such as palladium, to a hydrogen-measuring instrument such as an ionization chamber, for example, and is determined by the instrument. The measured concentration of hydrogen is thus a measure of the alcohol present in the breath sample.
The known device has the drawback that the air sample is first collected and then has to be subjected to pyrolysis. Different instruments must be used for the sampling and the pyrolysis, which requires a complicated procedure, and in addition, high energy consumption for the pyrolysis furnace as well as expensive measuring circuit for the detector. The requirement for electrical energy, both for the pyrolysis and for the measuring instrument, makes the method dependent on electrical supply systems or heavy, bulky units or batteries. Because of this, it is impossible to design a complete portable determination system that is both light in weight and easy to operate on the one hand, and on the other hand, requires the smallest possible amount of energy for operation.
Collecting the determinable pyrolysis products followed by measurement in one process directly during the sampling is impossible, but separate operating steps with intermediate steps of differing lengths are always necessary. An amount of pollutants that is not insignificant may remain adsorbed in the collector during the necessary desorption, which reduces the yield.
It is also possible to determine various pyrolysis products in the known device only when an appropriate permeable membrane is provided between the pyrolysis furnace and the measuring instrument.